The body of a conventional retractable knife 50, as shown in FIGS. 6 and 7, includes a main portion assembled from casings 52 and 54. A slot is longitudinally defined in the top face of the main structure and a protruding tip 56 can be pushed back and forth therein. A mount for fixing a blade 60 is integrally formed with the protruding tip 56. The blade 60 is retractable by pulling the protruding tip 56 to the back of the slot.
The conventional retractable knife is convenient for users to cut items such as papers, but is inconvenient in that the casings 52, 54 are securely attached by a screw 58, making it difficult to replace the blade. To replace the blade 60, a user has to first unscrew the screw 58, take out the blunt/unsuitable old blade 60, fit the new blade 60 into place and then screw in the screw 58 to secure the two casings 52, 54. The present invention provides a creative and novel means for solving the problems mentioned above.